Nucleophilic Ring Opening of Cyclopropane Hemimalonates Using Internal Brønsted Acid Activation

The reaction of cyclopropanes, geminally disubstituted with one carboalkoxy and one carbohydroxy group, undergoes ring-opening reactions with indole nucleophiles under catalyst-free, hyperbaric (13 kbar) conditions. An internal hydrogen bond is postulated as the mode of activation obviating the need for the Lewis acid catalyst normally used for such donor–acceptor cyclopropane chemistry. These conditions avoid decarboxylation and yield useful adducts with the carboxylic acid group intact for further elaboration.